(1) Field of the Invention
This invention relates to hybrid arrangements, and more particularly to transducer coupling, transmission level equalizing and to side-tone balancing circuits of the type useful in subscriber telephone sets.
(2) Descripton of the Prior Art
Present day two-wire subscriber telephone circuits are almost universally arranged in a hybrid configuration and are of the anti-side-tone type. The bridge transmission circuits shown in FIGS. 2, 3, 4 in U.S. Pat. No. 3,517,138 issued June 23, 1970 to V. G. Burger are representative of the prior art. These circuits utilize center tapped transformers in order to provide optimum power transfer through impedance matching between the transmitter, receiver, line and balance network. However, these circuits can only be used with high quality, high efficiency receivers. Lower efficiency receivers require greater power which can be provided to the receiver by using an unbalanced transformer. Such additional receiver power is provided only at the expense of decreased transmitter power.
Accordingly it is an object of the present invention to provide a novel technique of utilizing low cost, low efficiency loudspeaker type receivers in telephone substations without sacrificing transmitter efficiency.